The present invention relates to a pulsation type secondary air introducing apparatus in an internal combustion engine chiefly used for a vehicle.
A previously known secondary air introducing apparatus utilized on an engine body having an intake manifold, an exhaust manifold and an air cleaner provided at the upstream end portion of the intake manifold comprises a secondary air introducing passage communicating between the air cleaner and the exhaust manifold. A check valve is interposed in the passage arranged to operate in response to a pulsation pressure in the exhaust manifold to feed secondary air thereinto. Additionally, in the foregoing apparatus, there has been proposed an arrangement as shown in FIG. 1, for instance, wherein an expansion chamber c is interposed in the passage a so as to be located on the upstream side of the check valve b. This is so that there may be obtained a predetermined flow rate of secondary air in the passage a. There may also be obtained a silencing effect. The apparatus with this arrangement, however, has the disadvantage that the expansion chamber c must be comparatively large in volume. Consequently, this requires a comparatively large space in the engine compartment of a vehicle.
Especially, in the case of an exhaust pulsation type secondary air introducing apparatus, when it is necessary to introduce secondary air at a high speed rotation of the engine such as in the case of deceleration thereof, it is difficult to assuredly obtain a predetermined flow rate of the secondary air. This is delicately influenced by the length of the secondary air introducing passage a, the volume of the expansion chamber c and the position of the chamber c on the passage a. More in detail, in the case that the chamber c is 350 c.c. in volume, for instance, it often happens that the secondary air flow rate does not reach a predeterminedly aimed one if the length of a connecting tube A between the chamber c and the valve b is not proper. The relation therebetween is as shown by a curve d in FIG. 2. In such a case the silencing effect becomes minimal. When the chamber c is 600 c.c. in volume, for instance, it is shown by a curve e in the same Figure. Thus, the aimed at flow rate can be obtained. Also, the silencing effect is good regardless of the length of the tube A. To sum up, the volume of the chamber c must be larger than 600 c.c., for instance, resulting in the foregoing inconvenience.